The present invention relates to an ultrasound diagnostic apparatus displaying an ultrasound image and a reference medical image. The present invention also relates to a method of displaying a medical image thereof.
A conventional ultrasound diagnostic apparatus can display a real-time ultrasound image based on an echo signal acquired by transmitting an ultrasound wave from an ultrasound probe. For example, WO2004-098414 discloses an ultrasound diagnostic apparatus which displays a real-time ultrasound image and a reference medical image such as an X-ray CT (Computed Tomography) image and an MRI (Magnetic Resonance Imaging) image of the same cross-section in relation to a subject.
This ultrasound diagnostic apparatus identifies a region corresponding to a location of an ultrasound image and displays the reference medical image for the corresponding region in the volume data acquired by an X-ray CT apparatus and an MRI apparatus based on the location of an ultrasound probe detected by a location sensor. Thus, whenever the ultrasound probe is moved, the reference medical image and the ultrasound image are automatically and constantly displayed so as to follow the moving ultrasound probe. Therefore, the ultrasound image and the reference medical image can be easily compared.
However, in order to automatically display the real-time ultrasound image and the same reference medical image, it is necessary to identify a location relationship between an ultrasound image and a reference medical image about the coordinate systems. Therefore, a location alignment is performed to determine a location relationship between an ultrasound image and a reference medical image about the coordinate systems.
Hereinafter an example of aligning a location is explained. First, an arbitrary cross-section of a reference medical image is displayed by operating an operation device based on volume data of the reference medical image previously acquired from a subject. Ultrasound waves are transmitted to a subject, their echoes are received and a real-time ultrasound image of arbitrary cross-section is displayed.
Then, the operator tries to compare the real-time ultrasound image and the reference medical image, and moves the location of an ultrasound probe, and operates the operation device. Then the same cross-sections of the ultrasound image and the reference medical image finally are displayed. At this time, the displayed ultrasound image and reference medical image are the cross-sectional images of a characteristic portion, such as a branched region of blood vessel. Once the same cross-sections of the ultrasound image and the reference medical image are displayed, the operator indicates the characteristic portions of the ultrasound image and the reference medical image that seems to be indicating the same location on the subject with a cursor. Thus, the same portions of the coordinate systems of the ultrasound image and the reference medical image are identified, and the location relationship between the ultrasound image and the reference medical image about the same coordinate system is identified.
When the ultrasound diagnostic apparatus operator who is unaccustomed to the X-ray CT image or the MRI image performs such location alignment, one may not be able to grasp which section in the subject a reference medical image is even if the reference medical image is displayed. In some cases, finding a cross-section of the reference medical image having a characteristic region for location alignment takes a longer time, and displaying the same cross-sections of the reference medical image and the ultrasound image takes a longer time.